The Earth Science Picture of the Day (EPOD) highlights the diverse processes and phenomena which shape our planet and our lives. EPOD will collect and archive photos, imagery, graphics, and artwork with short explanatory captions and links exemplifying features within the Earth system. The community is invited to contribute digital imagery, short captions and relevant links.

Shark Teeth

The photo above shows a huge, ebony colored tooth of an ancient Cenozoic Era shark known as a megalodon. On top of it are two teeth from a modern era great white shark found on a California beach. Fossils indicate that megalodons reached a length of 52 ft (16 m); this compares to a length of 20 ft (6 m) for an exceptional great white shark. A shark's tooth is one of the most commonly found fossils since sharks go through several sets of teeth during their life. Their teeth are lost routinely but new ones constantly grow in to replace the ones that are surrendered.

The great white sharks at the left were photographed when I went on a cage-diving expedition off Guadalupe Island, Mexico. I was on deck and not in the cage while these shots were taken. The sharks were ravenously feeding on tuna.

Below, the remains of a whale washed ashore at Ocean Beach in San Francisco in September 2010 show bite marks left by great white sharks. Though the species of whale couldn't be identified, it was easy to tell that the bite marks were from a great white. A 2008 study determined that a great white shark specimen 20 ft (6 m) in length could exert a bite force of over 4,000 lbf (18,000 newtons), more than enough to cut through bone but not as forceful as the bite of a tiger shark or that of a Nile crocodile.

Oh, the shark, babe, has such teeth, dearAnd it shows them pearly whiteYa know when that shark bites, with his teeth, babeScarlet billows start to spread....